Method of making boiler tubes and the like



Nov. 5, 1940. T. E. MURRAY 2,220,579

METHOD OF MAKING BOILER TUBES AD THE LIKE Filed Deo. 28, 1934 2Sheets-Sheet l BY /y/ ATTORNEYS No-v. 5, 1940. T. E. MURRAY 2,220,579

METHOD OF MAKING BOILER TUBES AND THE LIKE Filed Deo. 28, 1934 2Sheets-Sheet 2 ATTORNEYS Patented Nov. 5, 1940 METHOD F MAKING BOILERTUBES AND Thomas E. Murray, deceased, late of Brooklyn, N. Y., by JohnF. Murray, Joseph B. Murray, and Thomas E. Murray, Jr., executors,Brooklyn, N. Y., assigner to Metropolitan Engineering Company, Brooklyn,N. Y., a company of New York Application December 28, 1934, Serial No.759,459

12 Claims.

In certain prior patents (for example, No. 1,844,407,'February 9, 1932)there are disclosed boiler furnace walls composed of finned tubes; thatis to say, tubes with anges extending continuously over the exposedportions, the tubes being erected alongside of each other with theflanges lling the spaces between them and forming a wall whichv ispractically closed to prevent the passage of gases or any substantialquantity of radiant heat from the combustion within.

Such boiler furnaces are iired most frequently with coal dust, or it maybe oil or gas, producing an intense degree of heat. y

In actual practice such anges have been welded continuously along thelength of such tubes by arc welding (that is, by depositing along thejoint welding metal melted by the electric arc) and this method lhasintroduced internal strains in' the tube and also in the flange. Ameasurement of such a tube about 20 feet long would show a contractionof a considerable fraction of an inch in length after the application ofthe anges, indicating a very high degree of strain. Such strains havecaused the tubes in some cases to split in use and have rendered thefree edges of the flanges moresusceptible to oxidation at the hightemperature prevailing, so that they have burned oiifl rapidly and couldnot be made in the beginning of the desired width.

The disadvantages of the continuous flange are set out more fully inapplication Serial No. 550,903, led July 15, 1931, disclosing thesubstitution for the continuous fin of a number of separate projectionsspaced slightly apart and providing a substantially unbroken wall.

rIhe present application is directed to the process of producing suchunits, that is, boiler tubes and the like with ilanges which for-al1practical purposes form a complete wall, without the strains involved inthe application of a continuous n welded along its entire length to thetube.

The accompanying drawings illustrate designs of boiler tubing andmethods of production.

Fig. 1 isa side elevation of a i'ln tube for the wall of a Murray typeof boiler.

Fig. la is an enlargement of a portion thereof to illustrate theseparation of the iin into a'number of small separate projections.

Figs. 2 and 3 are elevations of a tube in process of application ofprojections thereto;

Fig. 4 illustrates diagrammatically the weld-v ing operation.

Fig. 5 is a perspective of one of the projec- 55 tions before welding itto the tube. g

Figs. 6 and 7 are, respectively, la horizontal section and an elevationof the upper part of a water wall.

Fig. 8 is a view similar to Fig. 1 of another wall of a boiler tube.

Fig. 9 is a perspective of the upper end of a tube showing a differentdesign of the projections.

Tubes for boilers, super-heaters, economizers and various other heatexchangeapparatus are sometimes straight from end to end and are oftencurved in various ways along their length. The present invention isapplicable to all such shapes and has particular advantages inconnection with tubes that are curved. In Fig. 1, for example, there isa tube II having the main portion of its length straight and having itstwo ends Ibent in the same direction at a right angle for connection todrums or headers. The tube I2 of Fig. 8 has a slight bend at its upperend for connection to a steam drum I3, and its lower end bent in theopposite direction for connection to a headerl I4; the intermediateportion may also be bent at about the middle. Both these tubes areprovided with ns, designated as a whole by the numeral I5, extendingover the portions of their length which are exposed to the heat.

In making up tubes of this character into boiler walls (Figs. 6 and 7)they are arranged side by side, spaced apart from each other and withtheir nns abutting or overlapping so as to practically close the spacebetween the tubes against the passage of heat to the outside wall I6, orto any outside insulation that may be provided.

It has been found that where such ilns are welded in a continuous stripover the whole or any substantial length of the tube, there are strainsset up in the tube and in the strip which weaken them and sometimescause cracks in the iin or in the tube under the conditions of use asabove explained. It is proposed, therefore, to weld each fin in asuccession of steps along the length of the tube applying the n inseparate sections of such short length as to avoid the prev viousdifliculties. 'I'hey may be spaced so closely to each other as toconstitute in effect a complete wall without losing the advantage ofapplying them separately. Therefore, the fins I5 are composed ofseparate projections or segments I'I spaced as closely together aspossible without interfering substantially with each other when they aredistorted by the heat of the furnace and by the differences intemperature between the welded ends and the free ends thereof. `It hasbeen found in practice that projections of this sort can be made toextend farther outward from the tube than the old continuous ns and thatthey have a longer life and impose less strain upon the tubes than inthe old arrangement. 'Ihey are also advantageous in the making of benttubes of the shapes illustrated, for example, in Figs. 1 and 8. Acontinuous n would have to be bent with the tube, of course. It is mucheasier to bend a fin made up with a line of separate small segments andimposes less strain .on the parts.

In the case illustrated in Figs. 1 and la there is assumed a steelboiler tube of 4 inches outside diameter and about isa of an inch inthickness and projections which are 3 inches Wide (the radialdirection), 1 inch long (the direction lengthwise of the tube) and 1/4inch thick, spaced apart from 116 inch to f8 inch. Such tubes are fairlydescribed as long, small-diameter thin- Walled tubes. The invention isapplicable, however, to various other kinds and sizes of tubing and toprojections of various other dimensions and spacing. See for example,Murray & Lawrence Patent 1,929,444, October 10, 1933, illustratingvariations in structure, and Hoer Patent 1,968,079, July 31, 1934,illustrating an automatic machine for applying the projections.

The electric resistance methods of welding, which are probably the mostconvenient in this particular work, involve the passage of a currentthrough the tube and the end of the projection. In such methods there isa softening of the tube at the joint. For this reason, as well as forthe considerations stated above, it is desirable to limit the totallength of the tube covered by one welding operation. vIt is preferableto keep with, y

in a three inch length of the tube, assumingthe ordinary boiler tubeabove described. Within this length there may be applied at oneoperation either a single projection or iin-segment of about threeinches length, or several such segments totaling about three inches.

The projections, therefore, are applied either one at a time along theline (simultaneously at opposite sides of the tube where two such insare desired), or in groups of such a small number as not to exceed thelength of tubing which will retain its form under the conditions of heatand pressure.

For example, in Fig. 2, the projections l1 are applied in groups ofthree at a time which, assuming the particular dimensions above stated,would involve a length of tubing of slightly over three inches. Theoperation may be performed simultaneously at two or more points in thelength of the tube as illustrated by a second group of threeprojections. The spacel I8 must be maintained at such length that theheat applied at the two working points shall not be transmitted in anysubstantial degree from one to the other. Fig. 3 shows a second group ofthree projections applied following each of the two starting points.These operations are continued until the entire desired length iscovered as in Figs. 1 and 8.

Fig. 4 illustrates a suitable electric resistance welding method. Thetube l l is held clamped in the two parts i9 of a positive electrode.The projection il (or .group of such projections) is clamped between thetwo parts 2li of the negative electrode. The parts are brought intocontact, as illustrated, and the lcurrent passed between them. rihey maybe slightly separated to form sparks, as in the ordinary asli method,and thus softened or may be softened by the use of a high volume ofcurrent passed for a very brief time as in the Murray method., When theyare suciently heated the current is cut oi and the parts pressedtogether in the direction of the arrows and thus welded.

In these welding methods the inner end of the projection Il is usuallyformed with a tapered portion 2| which is taken up or extruded orsqueezed out in the Welding operation, leaving the welded contact areaequal to or greater than that of the welded end of the projection.

Fig. 9 illustrates a diierent style of projection In making bent tubes,the projections are applied throughout the whole or the desired portionof the length of the tube while the latter is straight. When the heat ofwelding is dissipated the tube is bent. 'I'he interrupted n offers nosubstantial resistance to bending in the plane transverse to the fin. Inthe few cases where the t'ube requires bending in the plane of the fin,the projections may be spaced or shaped so as not to contact with eachother within the desired degree of curvature of the tube.

What is claimed is:

1. A process for making tubes for boiler walls with practicallycontinuous ns secured thereto which consists in separately welding tothe tube 1in-segments spaced slightly from each other to compensate forirregularities of expansion and contraction in portions of said segmentsadjacent to the tube as compared with portions remote from the tube,with the segments in line and in suoient proximity to each otherlengthwise of the tube to provide a substantially unbroken wall whenused in connection with other similar tubes.'

'2. A process for making tubes for boiler walls with practicallycontinuous finssecured thereto which consists in separately welding tothe tube iin-segments spaced slightly from each otherV to compensate forirregularities of expansion and 'contraction in portions of saidsegments adjacent to the tube as compared with portions remoteffrom thetube, with the segments in line and in sufficient proximity to eachother lengthwise of the tube to provide a substantially unbroken wallwhen used in connection with other similar tubes, said processcomprising the welding of the segments to the tubes by an electricresistance method involving the passage of a heating current through thetube and the segments and the pressing of them together, the segmentsbeing applied in a succession of steps, each step embracing such a shortportion of the length of the tube as to avoid heating the wall thereofsuciently to permit substantial distortion under the pressure applied.

3. The process of claim 1, the segments being applied in a succession ofsteps along the length of the tube one at a time so as to avoid heatingthe tube over such a length as to permit substantial distortion underthe pressure applied.

4. 'Ihe process of claim 1, the segments being applied in a successionof steps not greater than about three inches in length.

5. The process of claim i, applying said segments simultaneously atopposite sides of the tubes.

6. The process of claim 1, applying the segments simultaneously atpoints in the length of the tube so far apart as to avoid thetransmission of any substantial quantity of heat from one to the other.

'7. I'he process of claim 1 appliedv to a steel boiler tube of the orderof about four inches diameter and of an inch in thickness, and thesegments being applied over a continuous length of not more than aboutthree inches.

8. The process of claim 1 applied to the tube while it is straight, andthereafter bending the tube.

9. 'I'he process of claim 1 applied to the tube while it is straight,and thereafter bending the tube in a plane at right angles to that ofthe projections.

10. A process for making tubes with separate projections securedthereto, said process comprising the welding of the projections to thetubes by an electric resistance method involving the passage of aheating current through the tube and the projections and the pressing ofthem together without an internal mandrel but solely against theresistance of the tube wall, the projections being applied in asuccession of steps along the length of the tribe, each embracing such ashort portion of the length of the tube as to avoid heating the wallthereof sufliciently to permit substantial distortion under the pressureapplied.

11.- A process of making tubular umts for boiler Walls and the likecomprising a long, smalldiameter thin-walled steel tube with separateprojections secured thereto, said process comprising the welding of theprojections to the tubes by an electric resistance method involving thepassage of a heating current through the tube and the projections andthe pressing of them together, applying the projections in a successionof steps along the length of the tube not greater than about threeinches in length.

12. A process of making tubular units for boiler walls and the likecomprising a long, smalldiameter thin-walled steel tube with separateprojections secured thereto, said process'comprising the welding of theprojections to the tubes by an electric resistance method involving thepassage of a heating current through the tube and the projections andthe pressing of them together, applying such projections simultaneouslyat opposite sides of the tube.

JOHN F. MURRAY.

JOSEPH B. MURRAY.

THOMAS E. MURRAY, Jn. Eecutors of the Estate of Thomas E. Murray,

Deceased.

